Laserfiche WebLink
• Page 4-5: The text states"Deleterious change in saturated groundwater or surface water <br /> chemistry is not expected as a result of AM-11 activities." Does this also apply to <br /> shallow groundwater in the region?Have you considered adding a shallow <br /> groundwater monitoring well(s) in Poverty Gulch? If not, how will you know <br /> whether a deleterious change to shallow groundwater chemistry has occurred due to <br /> increased mining activities near Poverty Gulch? <br /> RESPONSE. The deeper well currently installed in Poverty Gulch (PGMW--2) has never <br /> produced water and no water was encountered during drilling. As such water in the <br /> shallow alluvium is not expected. That being said, DRMS's comment is noted and CC&V is <br /> evaluating the technical merits of installing a shallow well in Poverty Gulch. <br /> 4.6—Hydrology <br /> 4.6.1 Surface Water <br /> • Page 4-8 - Grassy Valley: The text states that the proposed increase to the final crest <br /> elevation of ECOSA to 10,960 feet is not expected to impact surface water quality of <br /> Grassy Valley nor will it impact the locations of current monitoring stations in the <br /> drainage. However, in Volume II, you discuss the toe seepage occurring from ECOSA(on <br /> the portion located outside of the diatreme) during high infiltration events. Do you <br /> anticipate an increase in seepage intensity with a greater load being placed on <br /> ECOSA with AM-11? How will you work to minimize impact to the Grassy Valley <br /> drainage? <br /> RESPONSE.No. The increased thickness of ECOSA provides a greater attenuation <br /> potential for infiltration, and so tends to reduce, rather than intense, seepage. <br /> In any event, the ECOSA underdrain system is designed to conduct water in excess of that <br /> which will seep through the foundation clay till from areas underlain by Precambrian <br /> rock to areas underlain by diatremal rock. <br /> Monitoring in Grassy Valley will continue to identify potential impacts should they occur. <br /> If impacts are identified, CC&V will mitigate. <br /> 4.6.2 Groundwater <br /> • Page 4-10 - Poverty Gulch: The text states"The underground workings that will be <br /> accessed by the Chicago Tunnel portal lie within the diatreme and have been dewatered <br /> by the historic drainage tunnels",and that"no impacts are anticipated to the <br /> groundwater quality in Poverty Gulch as a result of AM-11". However, under Section <br /> 4.5 Geochemistry,page 4-5,you mention that the underground exploration may <br /> penetrate the zone of saturation in the northern portion of the diatreme. Please explain <br /> this discrepancy. <br /> RESPONSE. The maximum expected depth for Amendment]] underground operations <br /> is 750 feet. There is little to no potential for underground mine operations to intercept the <br /> regional water table in this area. <br /> 4.6.3 Summary <br /> • Page 4-12: The text states"the presence of historic mine features in many of the <br /> drainages appears to have some influence on the current surface water quality". Please <br /> describe in particular what impact(s)you are referring to. Furthermore, how do <br /> you differentiate impact from historic mine features from impact from mining <br /> activities occurring under this permit? <br /> Page 27 of 28 <br />